Enhanced photothermoelectric conversion in self-rolled tellurium photodetector with geometry-induced energy localization

Photodetection has attracted significant attention for information transmission. While the implementation relies primarily on the photonic detectors, they are predominantly constrained by the intrinsic bandgap of active materials. On the other hand, photothermoelectric (PTE) detectors have garnered substantial research interest for their promising capabilities in broadband detection, owing to the self-driven photovoltages induced by the temperature differences. To get higher performances, it is crucial to localize light and heat energies for efficient conversion. However, there is limited research on the energy conversion in PTE detectors at micro/nano scale. In this study, we have achieved a two-order-of-magnitude enhancement in photovoltage responsivity in the self-rolled tubular tellurium (Te) photodetector with PTE effect. Under illumination, the tubular device demonstrates a maximum photovoltage responsivity of 252.13 V W−1 and a large detectivity of 1.48 × 1011 Jones. We disclose the mechanism of the PTE conversion in the tubular structure with the assistance of theoretical simulation. In addition, the device exhibits excellent performances in wide-angle and polarization-dependent detection. This work presents an approach to remarkably improve the performance of photodetector by concentrating light and corresponding heat generated, and the proposed self-rolled devices thus hold remarkable promises for next-generation on-chip photodetection.


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The relationship between the photogenerated voltage and frequency of the device can be expressed by the following formula: [13] () =  1 + 4π Here, V0 represents the value of photovoltage measured under continuous irradiation, f represents the corresponding test frequency, and τ represents the response time.In Figure S9, the gray line is the fitting curve according to this formula.Here, the frequency value fC corresponding to 0.707 V0, namely the -3 dB bandwidth, is 205 Hz.And τ is calculated to be 760 μs, which is consistent with the experimental result in Fig. 1f.
The Tauc plot is calculated on the basis of the FTIR absorption spectrum to determine the optical bandgap: [14] (ℎ) ⁄ ∝ (ℎ −  ) Here, α is the absorption coefficient, h is the Planck constant, v is the frequency, Eg is the optical bandgap energy, r is 2 in the case of indirect interband transition.
The secondary electron cutoff spectrum in the inset of Fig. 2f displays that the Fermi level (EF) is -2.28 eV, followed by: [15]  = ℎ −  .
Here, Ecutoff refers to the binding energy.Based on the valence-band spectrum in Fig. 2f, the valence band maximum (VBM) position of Te is calculated to be -2.48eV.Considering the optical band gap of 0.37 eV, the conduction band minimum (CBM) is estimated to be -2.11eV.

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Note S4.Strain in TTDs calculated by Raman peak shift.
As the lattice expands, E2 and A1 modes obviously shift, as shown in Fig. 2g.The strain therein thus can be estimated by the shift of Raman mode (∆), which is related to the shift of phonon frequency: [16] ∆ where  is the strain in Te and ω refers to  and  of unstrained Te.The p and q are linear interpolations that can be extrapolated from previous research. [17]Here, ( + 2) is 2.44 × 10 s and ( + 2) is 1.70 × 10 s .The compressive strain in the TTDs is calculated to be 0.35% or 0.50% by using the shift of A1 or E2 mode under 532 nm laser illumination.

Table S1 .
Testing results of Seebeck coefficient of Te layer at room temperature.

Table S2 .
Comparison of photovoltage responsivities of PTE detectors with different working wavelengths reported in recent literature.